For the mounting of a wheel on the hub of a motor vehicle bolted connections are conventionally used. Heretofore, the most common way to secure the wheel to the radial flange of the hub is to provide conventional threaded bores in the radial flange of the hub and through bores formed in the wheel. The wheel, a flange of the brake rotor and the radial flange of the hub are brought axially close to one another and a set of bolts are fitted into the aligned bores of these three elements. The bolts are screwed and tightened in the threaded bores of the hub.
The motorcar industry is facing an ever increasing demand for weight reduction in motor vehicle components for the sake of cutting down fuel consumption and exhaust emissions. In order to reduce the overall weight of the wheel and, in particular of the rotating mass, the hub flange may be partially made of a lighter material than the steel constituting the central part or tubular core of the hub. Typically, the flange can be made of light metal alloys (such as aluminum, titanium, magnesium), metal matrix composites, polymers, fiber reinforced polymers. The core of the hub is made of a high toughness metallic material, such as a bearing grade steel or a steel with a low carbon content. The coupling between the core of the hub and the lighter flange is made alternatively by interference form coupling with, or by overmolding.
Patent publication WO 2008/147284 A1 discloses a bearing ring composed of two different materials joined together as a single piece, namely a first high toughness material, such as a bearing grade steel, which form the raceways, and a second light material, such as a light metal, which forms the remaining part of the ring, including an outer flange for mounting the wheel.
It is known that the aforesaid light materials generally have a lower mechanical strength than that of steel which is used conventionally.
The mounting of the wheel connecting bolts in bores formed directly through a light metal or light metal alloy flange involves a high concentration of stress, which is inadmissible on surfaces of reduced area of a metallic material having a hardness which is much less than that of steel. Because of this, there is the risk that the bolts may gain some play within the bores of the flange and become free to rotate and/or perform undesirable axial displacements.
An object of the invention is to provide a steady threaded connection for the wheel mounting bolts, in a flanged ring of the aforementioned type, having a lightweight metal flange for mounting a motor vehicle wheel.